46 - PRACTICAL ORGANIC CHEMISTRY If Wis the weight of salt, w the weight of silver, and ;/ the basicity of the acid, the molecular weight of the silver salt is determined4from the following- formula :— The molecular weight of the acid is then obtained by deduct- ing n atoms of silver and adding n atoms of hydrogen. ^Example— 0-3652 grm. silver benzoate gave 0*1720 grin. silver. 108 X - 108 + I = 122-2. 0'I72O Calculated for C7H602 ; M = 122 Molecular Weight of Organic Bases Determination by means of the Platinum Salt. — The organic bases form, like ammonia, crystalline chloroplati- nates with platinic chloride of the general formula B2H2,PtClfl. By estimating the amount of platinum present in the salt, it is possible to calculate the molecular weight of the platinum corn- pound, and consequently that of the base. Dissolve about i gram of an organic base (brucine, strych- nine, guinine, &c.) in 10 c.c. of a mixture of equal volumes of concentrated hydrochloric acid and water. To the clear hot solution add excess of platinic chloride and let it cool. Yellow microscopic crystals of the chloroplatinate of the base separate. (If the chloroplatinate of the base is very soluble in water, such as aniline, it must be washed with strong hydrochloric acid, pressed on a porous plate and dried in a vacuum-desiccator over solid caustic potash.) Filter on the porcelain funnel with the pump and wash three or four times with small quantities of cold water. Press the precipitate down and dry on a porous plate in the vacuum -desic- cator. When thoroughly dry, weigh out about 0-5 to i gram of the compound into a porcelain or platinum crucible, and heat gently with the lid on, and then more strongly until the organic matter is completely burnt away. Cool the crucible in the desio ea.or and weigh.